In radar systems, the range of a target is proportional to the time between a transmitted pulse and target return signal. In medium and high PRF systems, range ambiguities arise because the particular transmitted pulse to which the target return signal is associated is unknown. The range ambiguity problem may be resolved by use of multiple PRFs, as generally discussed in Skolnick, "Introduction to Radar Systems", McGraw Hill, New York, 1962.
More recent multiple PRF range resolving techniques include such schemes as the Chinese remainder theorem or the shift register approaches. The Chinese remainder theorem approach is described in Skolnick, "Radar Handbook", section 19, pp. 19-16, McGraw Hill, 1970. To calculate target range by using the Chinese remainder theorem, all combinations of target return signals in one ambiguous range interval for each PRF must be examined for the existence of a consistent unambiguous range. The number of combinations which must be examined increases as a function of the number of target return signals raised to the power determined by the number of PRFs. A typical computer loading equation for the Chinese remainder theorem approach, which provides an indication of the number of computations required by the electronics, is given by 2N.sup.2 (4+5N), for a three PRF system, where N is the number of range intervals between transmissions. Table 1 below shows the number of computations required as a function of the number of target return signals using the Chinese remainder theorem approach.
The shift register technique cyclically shifts quantized tables of target return signals for each PRF, and when target return signals appear simultaneously at the top of each table, an unambiguous target range is determined. The number of computations performed is proportional to the number of range intervals in the maximum unambiguous range. The number of computations required for the shift register approach is generally given by the equation JT + 18NT, for a three PRF system, where J is the number of range intervals between transmissions, and T is the number of ambiguous range zones in the maximum unambiguous range. Table 1 also shows the number of computations required for the shift register technique with respect to the number of targets viewed by the radar system.
______________________________________ Number of Computations Targets Chinese Shift Reg. ______________________________________ 1 18 1260 3 342 1800 5 1450 2340 10 10800 3690 ______________________________________
Thus, in conventional techniques, the number computations increases more rapidly than the number of targets. With present digital signal processors, it is computationally inefficient in terms of equipment and/or time to perform either of the above two conventional techniques, and a method which exhibits reduced loading requirements would be a significant advance in the art.